1. Field of the Invention
The present invention relates to an engine.
2. Description of the Related Art
Japanese Unexamined Patent Publication No. 63-143349 discloses an internal combustion engine having an intake passage, a throttle valve arranged in the intake passage, and a fuel injector arranged in the intake passage downstream of the throttle valve for injecting fuel in the intake passage. The engine is provided with an air-flow control valve arranged in the intake passage between the throttle valve and the fuel injector. The air-flow control valve is closed during an engine starting operation, and is opened after the engine starting operation is completed.
In a typical engine, when the engine is to be started, a certain quantity of air exists in the intake passage downstream of the throttle valve, even if the throttle valve is substantially closed. If this air is drawn into a combustion chamber of the engine, the air-fuel ratio of an air-fuel mixture formed in the combustion chamber is made lean and it causes an improper combustion. As a result, an exhaust gas from the engine contains a large quantity of unburned hydrocarbons (HC). In particular, when the engine includes a surge tank in the intake passage downstream of the throttle valve, a larger quantity of air will be drawn into the combustion chamber at the starting operation of the engine, to further increase the unburned HC in the exhaust gas. To solve this problem, in the above-mentioned engine, the air-flow control valve is arranged in the intake passage between the throttle valve and the fuel injector, and the valve is substantially closed during the engine starting operation, to prevent the combustion chamber from drawing in a large quantity of air.
In the above-mentioned engine, when the engine starting operation is completed, the air-flow control valve is opened to secure a proper amount of air for combustion. The air-flow control valve has a valve element with an axis about which the element is rotatable, and thus, to open the air-flow control valve, the valve element is rotated about the axis thereof. If a rotation direction about the axis of the air-flow control valve is selected so that air flowing through the air-flow control valve is biased toward a wall of the intake passage opposite to the fuel injector by the valve which is at an intermediate open position between a closed position and a full open position thereof, the air will not properly hit and atomize fuel injected from the fuel injector. JPP '349 provides no suggestion about biasing an air flow by the air-flow control valve when the valve is at the intermediate open position.